1. Field of the Invention
Aspects of the present invention relate to an organic light emitting diode (OLED) display. More particularly, aspects of the present invention relate to an OLED display in which a contact error of a dual-capacitor can be prevented.
2. Description of the Related Art
When electrons and holes are injected in an organic material through an anode and a cathode, excitons are formed by a recombination between the electrons and the holes. The excitons emit energy while being transited to a ground state, and light having a specific wavelength is generated by the emitted energy. A self-emissive display using the above property is called an organic light emitting diode (OLED) display.
OLED displays do not require a separate light source such as a backlight, and thus, OLEDs have advantages of reduced power consumption in comparison with other display technologies such as LCDs. Furthermore, since OLED displays provide a wide view angle and have quick responsiveness, OLED displays are gaining prominence as a next generation display.
OLED displays are classified as passive matrix displays and active matrix displays. Recently, the active matrix displays that can realize low power consumption and quick responsiveness have been developed.
In the active matrix OLED display, a pixel area at which an image is actually displayed is formed on a pixel substrate. Metal lines and data and scan drivers that drive the pixel area in response to signals input through pads of the metal lines are formed around the pixel area.
A plurality of pixels, each of which is a basic unit used in displaying the image, are arranged in a matrix pattern at the pixel area. An organic light emitting element is disposed on each pixel. The organic light emitting element includes red, green, and blue organic light emitting layers, and anode and cathode electrodes that are alternately formed between the red, green, and blue organic light emitting layers.
Thin film transistors (TFTs) coupled to the organic light emitting element are formed on each pixel so that the pixels can be independently controlled. The TFTs are classified into switching transistors that transmit switching signals and driving transistors that transmit driving signals to the organic light emitting element.
The pixel circuit may be a 2-transistor type pixel circuit having one switching transistor and one driving transistor. However, with this structure, a threshold voltage deviation is generated within a panel. This causes luminance dispersion. Therefore, a circuit that uses more than two transistors to compensate for the threshold voltage deviation has been proposed.
When more than two transistors are used, a capacitor is generally formed in a dual-structure to increase capacitance. For example, one electrode of the capacitor may be defined by a gate pattern and another electrode of the capacitor may be defined by the connection of an active pattern and a source/drain metal through a contact hole.
However, when the contact hole is not successfully formed due to particles generated during the manufacturing process, the source/drain metal may not be properly connected to the active pattern. In this case, the active electrode cannot function as an electrode of the capacitor and thus, the capacity of the capacitor is significantly reduced to be lower than normal capacity. Furthermore, this causes other collateral problems.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.